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Introduction to Physiology.docx

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Physiology 2130
Anita Woods

Introduction to Physiology Section 1.1 Objectives By the end of this section, you should be able to: • Define physiology • Define homeostasis • Describe negative feedback control systems. • List the levels of organization in the human body Section 1.2 What is Physiology? • Physiology is the study of function in living organisms. • It explores the mechanisms by which the organisms control their internal environments regardless of what happens in the outside (or external) environment. • Physiology also attempts to explain the physical and chemical factors responsible for both normal function and disease (also called pathology). Section 1.3 Homeostasis • Internal environment:  The fluid in which the cells of the body are bathed.  This essentially consists of the interstitial fluid and blood plasma—a region we will examine in more detail in module 2. • External environment:  The region outside the body.  The external environment also includes the space and contents of the digestive, respiratory, and urogenital tracts. • Homeostasis:  The maintenance of relatively stable conditions within the internal environment regardless of what is happening in the external environment. Section 1.4 Homeostasis (cont.) • Our body is capable of maintaining our internal environment so that our cells can function regardless of what is happening in the external environment. This is homeostasis. • The body maintains homeostasis using negative and positive feedback control mechanisms. Section 1.5 Negative Feedback Control Systems • Negative feedback control systems:  Found throughout the body and perform different functions such as maintaining body temperature and maintaining body fluid volumes.  All negative feedback control systems operate the same way to maintain homeostasis.  They contain a set point, a control center (also called an integrator), an effector, a controlled variable, and a sensor (also called a receptor) – shown below. Section 1.6 Negative Feedback Control Systems (cont.):  The simplest example of a negative feedback control system is the heating system in your house. The set point is the temperature at which the room is set (for example, 20°C or 68°F). The sensor/control center, which are combined in our example (this usually is not the case in the body), represent the thermostat. The effector is the furnace, and the controlled variable is heat.  This is a negative feedback system because the controlled variable (the heat), which is detected by the sensor, eventually shuts off its own production by the effector (the furnace). Section 1.7 Negative Feedback Control Systems (cont.): • Here is how negative feedback controls body temperature. The set point for body temperature is 37°C (98.6°F). This is the temperature that you want your body to maintain. Your actual body temperature could be different; it could drop on a cold day to 35°C (95°F). This actual body temperature would be detected by sensors in the nervous system which would signal a control center in a specific region of the brain called the hypothalamus. The control center would notice a difference between the set point (what you want) and the actual value of 35°C (95°F). The control center would then activate organs and systems (the effector) to generate heat (the controlled variable) by shivering and conserving heat by decreasing blood flow to the skin. • Once the body temperature rises back to 37°C (98.6°F), the control center would stop the shivering and would return the blood flow to the extremities. The opposite would happen if body temperature increased above the set point. The
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